A baghouse or fabric filter, whether it uses traditional bags with cages or pleated cartridge filters, is an air pollution control device that removes particulates out of air or gas released from commercial processes or combustion for electricity generation. Many different types of industrial companies use baghouses to control emission of air pollutants including power plants, steel mills, pharmaceutical producers, food manufacturers, and chemical producers. Depending on the process requirements and/or air flow to be cleaned, baghouses can range from a single compartment filter to a large multi-compartment filter. Baghouses are generally defined by their cleaning methods. The two major categories are off-line cleaning baghouses and on-line cleaning baghouses. Off-line cleaning refers to the type of baghouse where the compartment is isolated and does not filter dirty air during the cleaning process. The types of baghouses using off-line cleaning include shakers, sonic horns, pulse-jet, and reverse air.
For a shaker style baghouse, the compartment is isolated from dirty air at the start of the cleaning cycle and the bags in that compartment are mechanically shaken. The shaking breaks up the filtered cake and with no air flow through the compartment the cake drops into a hopper below the compartment. This style of baghouse may use up to four output and four additional inputs. The outputs would be to open and close the inlet and output isolation valves and the inputs would be switches to confirm the isolation valve position. Additional outputs may be required to initiate the shaking mechanism for each compartment.
The sonic horns style baghouse is similar to the shaker style with the exception that the cake is broken up by sound of the sonic horn instead of a mechanical shaking mechanism. This style of baghouse may use up to four output and four additional inputs. The outputs would be to open and close the inlet and output isolation valves and the inputs would be switches to confirm the isolation valve position. Additional outputs may be required to initiate the sonic horns for each compartment.
The pulse-jet style baghouse involves isolating the compartment and then the pulse-valves are fired to generate a blast of air down each bag in a row. The blast of air breaks the cake loose and allows it to drop to the hopper below. This style of baghouse typically has one solenoid valve for each row of bags. Larger baghouses may have split rows and may use two valves per row. The row valves are pulsed, which means they are on for only a fraction of a second to create the blast of air used for cleaning. In an off-line configuration, each compartment may use up to four additional outputs and four additional inputs. The outputs would be to open and close the inlet and output isolation valves and the input would be switches to confirm the isolation valve position.
The reverse air style baghouse involves isolation of the compartment from filtering dirty gases and a clean air source is sent in the reverse flow from the filter gas. Reversing the air flow breaks up the filtered cake and allows it to drop into the hopper. This style of baghouse may use up to four outputs and four additional inputs. The outputs would be to open and close the inlet and output isolation valves and the inputs would be switches to confirm the isolation valve position. Additional outputs may be used to open the clean air gates and initiate the clean air flow.
On-line cleaning refers to the type of baghouse where the compartment is cleaned while it continues to filter the dirty gas stream. The pulse-jet baghouse may be used in an on-line cleaning configuration. While the baghouse or compartment is filtering dirty gases, a blast of air is sent down each bag in a selected row. The blast of air breaks the cake loose. Because the compartment or baghouse is still filtering, the gas velocity may carry some of the lighter material to another bag while the heavier material falls into the hopper below. This style of baghouse typically has one solenoid valve for each row of bags. Larger baghouses may have split rows and use two valves per row. The row valves are pulse, which means they are on for only a fraction of a second to create the blast of air used for cleaning.
While there are several different types of baghouses as described above, the monitoring and control systems for controlling the baghouse cleaning cycle are similar across the different types. A series of solenoid valves and other mechanical apparatus may be used to pulse bags, isolate compartments, open/close valves, active/deactivate horns, and active/deactivate shaking mechanisms. As shown in the baghouse control system of FIG. 1, this typically involves long runs of wire from a controller 105 to each baghouse module. The modules may correspond to discrete input and output devices 110, such as valves, relays, switches, and the like as well as analog input and output devices 115, such as pressure control devices, temperature control devices, air flow control devices, valve positioning, and the like.
These long runs of wire can be expensive, however, and may make it more difficult to diagnose and troubleshoot problems. Safety may also be a concern when AC power is used due to support personnel handling the AC power in the field.
FIG. 2 illustrates a baghouse control system configuration where Input/Output (I/O) modules 220a, b, c are moved from the controller 205 to a location in the field closer to the discrete devices I/O 210 and the analog devices I/O 215. While this configuration reduces the amount of wiring required relative to that of FIG. 1, both power and communication wiring need to be run to each of the I/O modules 220a, b, c. The cabling running from the power source 225 to the I/O modules 220a, b, c are not run together with the communication wiring from the controller 205 and, therefore, additional conduit is required. Moreover, the relay modules for the controller 205 do not provide feedback on the status of the solenoid valves.